Clams Dwindle as CO2 Rises.

04/10/2010 17:14

The number of shelled creatures in the ocean is truly dizzying. And we need them -- they are keystone species for everything from building coral reefs to anchoring the ocean food chain to making a killer linguine and clam sauce.

But as carbon dioxide builds up in the atmosphere, ocean water becomes more acidic. And shellfish have trouble growing their shells.

Scientists have worried for years about ocean acidification affecting shelled creatures in the future, but according to a new study, it's already happening, and has been for over a hundred years.

Led by Christopher Gobler of Stony Brook University in New York, a team of researchers grew Northern quahog clams and Atlantic bay scallops under varying CO2 concentrations.

At 250 parts per million CO2, the shellfish grew vigorously, and at 750 ppm and higher they were crippled, feeble creatures with thin shells and weak connective tissues. No surprise there -- from coral to clams to microscopic foraminifera, shelled critters make their hard parts out of calcium carbonate (CaCO3). The stuff is tough as a rock (limestone is made primarily of calcium carbonate), but it dissolves instantly in acid.

What was surprising was how sensitive the animals were to increasing CO2. You see, 250 ppm of CO2 doesn't exist anymore -- it's a pleasant memory from a time before human ingenuity brought about the Industrial Revolution. In the scant century and a half since then, we've bumped atmospheric carbon dioxide up to 390 ppm. In the researchers' experiment, that was already enough to stunt shellfishes' growth and make their shells thinner.

What does that mean? It means if we want to keep eating mussels marinara, clams casino, or other alliterative seafood dishes, we'd better kick our carbon-emitting fossil fuels habit right quick.

Pollution, algae blooms, and rising temperatures all have roles to play in places where where shellfish stocks are declining. But as Gobler points out, efforts to restore populations to healthy levels might be harder than anyone thought, because the animals' shells won't be, well, hard enough.